The present application relates to an infrared optical system for use in a system of obtaining infrared images such as thermography or night vision imaging, and to an infrared imaging apparatus using the infrared optical system.
Far infrared rays are in the wavelength range from 8 μm to 12 μm, and are emitted from human beings, animals, and others as heat, i.e., as infrared rays. This makes the far infrared rays popular for use with imaging in dark places or observing temperature distributions, for example.
With an optical system gathering such far infrared rays, a glass lens often used for general visible light is not used due to the low transmittance thereof, and instead, germanium (Ge) is popularly used as a material that passes therethrough the infrared rays well. Germanium has a high refractive index of about 4, and the surface reflectance is thus high but the absorption index is closely zero. As such, with an appropriate antireflective coating, germanium may have the transmittance of 90% or higher.